Electron device



Jan. 12, 1937 F. MICHELSSEN 2,067,330

' ELECTRON DEVICE Filed Aug. 8, 1932 INVENTOR FRITZ MICHELSSEN ATTORNEY Patented Jan. 12, 1937 UNI-TED STATES PATENT OFFEQE ELECTRON DEVICE tion of Germany Application August 8, 1932, Serial No. 627,927 In Germany August 18, 1931 2 Claims.

The present invention relates to electron devices and is particularly related to a means for concentrating the electron stream within a cathode ray or X-ray tube.

5 It is known in the art that the production of sharply focused cathode-ray pencils of the kind utilized in Roentgen-ray tubes, Braun tubes and some other discharge vessels is attended with quite a number of practical difficulties. One effective means used in the prior art to concentrate the electrons in the discharge path has been disclosed by Wehnelt, and this scheme is extensively in use at present.

The arrangement used and disclosed by the prior art usually consists, for instance, of an anode provided with a diaphragm aperture, a heated filament and a cylinder which envelopes the filament and which by the action of its potential forces the electrons to fiow along a definite path or trajectory. The dimensions of the construction using this idea, however, must be so chosen that certain lines of force will be able to flow rectilinearly from the anode to the cathode of the tube. The anode potentials should not be completely screened off by the cylinder and they should not find a chance to reach the points of issuance of the electrons by circuitous routes.

Contradistinct from this well-known arrangement, the present invention, in which the aim likewise is to insure rectilinearity of the electric force-lines from the anode to the cathode, While curved force-lines are screened off, offers a number of technical advantages.

The essential features underlying the novel arrangement hereinafter to be disclosed have been illustrated by the accompanying drawing, wherein Fig. 1 represents one form of the tube including the features of the invention and wherein Fig. 2 discloses a modification of the structure shown by Fig. 1.

Now referring to the drawing, the features of the invention reside in mounting between the positively charged anode A and the cathode K being at zero potential, a third electrode S maintained 45 at a correspondingly high negative potential.

What is also feasible in this arrangement is to ground the anode A and to keep the cathode K and/or the screen sheet S at adequately high negative potentials. It is important that the 50 dimensions of anode A and screen electrode S should be so chosen that the anode potential will be able to act only across the apertures in the screening sheet, that is, for example, the grid sheet, while actions around the said sheet are 55 precluded by appropriate forms of construction.

If these planar or surface electrodes, for instance, of a shape as shown, extend to points at close proximity to the walls of the envelope of the vacuum vessel, then a similar diameter of both electrodes, that is, the anode A and concentrator screen S, is permissible.

While initially there may occur actions of the anode potential across the narrow gap between the edge of the screen sheet S and the glass tube Wall G for a brief instant, such cross-gap actions will be effectively suppressed by the negative charge that accumulates on the glass wall. If the electrodes are freely supported in the space inside the envelope and mounted at relatively great distances from the walls of the vessel, it will be necessary in order to insure satisfactory ray concentration to choose substantially smaller dimensions for the anode than for the concen trator electrode, with a view to eliminate all chances of electric force-lines coming to act curvilinearly.

The screen electrode S could also be made of wire gauze or network S, as shown by Fig. 2, rather than from a solid lamina. Actions of the anode potential across the meshes of the concentrator electrode are readily avoidable if the relationship between mesh size and opening is judiciously chosen.

It has been found that in order to insure satisfactory concentrating actions very definite demands must be fulfilled as regards the distances 0. and b, which represent the distance of the emitter from the screen and the aperture diameter, respectively. In order to secure sharply concentrated or focused ray-pencils, for which purpose the action of concentration could be effectively promoted and assisted by the constrictive action of a gas-filling, it is necessary that the distance a of the emissive body from the surface of the concentrator electrode should not be more than one-half the inside diameter 1) of the concentrator electrode.

Looked at from the manufacturing viewpoint, this simple disposition offers the advantage over the use of a Wehnelt cylinder that the making and mounting of a simple planar or surface-diaphragm is attainable by substantially simpler tool equipment than the complicated manufacture of cylinders in which the question of diameter, longitudinal dimensions and true circular form must be strictly fulfilled. Particularly advantageous in manufacture is the use of planar electrodes rather than cylinders whenever the point is to secure a fixed distance between a punctiform cathode and the concentrator diaphragm without unduly complicated auxiliary means. lihe attempt of fixing certain distances in the interior of a hollow cylinder is associated with certain difficulties, so much more so as the damaging of an oxide-cathode capable of electron emission even at low temperatures must be absolutely avoided by length measurements.

Using the novel arrangement hereinbefore disclosed in a Braun or cathode ray tube, then, if the tube is to be used for re-creating television pictures, the intensity of the cathode-ray pencil is controllable by variation of the potential of the concentrator electrode S.

Having now described my invention, what I claim and desire to secure by Letters Patent is the following:

1. An electron tube comprising an electron source, an anode electrode positioned in cooperative relationship with respect to the source, and

a narrow meshed wire gauze aperture-d concentrator electrode, the apertured electrode being positioned at a distance from the source of the order of one-half the diameter of the aperture.

2. An electron tube comprising an electron source, an anode electrode positioned in cooperative relationship with respect to the source, and a single apertured electrode adapted to be supplied with a negative biasing voltage, said electrode being entirely interposed between the anode and the source, the aperture being of a diameter D and spaced from the source by a distance w, and the relative relationship between b and a being such that FRITZ MICHELSSEN.

' Certificate of Correction Patent No. 2,067,330 January 12, 1937.

FRITZ MICHELSSEN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 15, claim 2, the equation should appear as shown below instead of as in the printed patent:

ine

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 6th day of April, A. D. 1937.

[SEAL] HENRY VAN ARSDALE, Acting Commissioner of Patents, 

